Sterilization

Sterilization may be defined as the complete destruction of all organisms, or their removal from materials by means of heat ,chemicals, irradiation or filtration methods.

Heat: The usual methods employed for the sterilization of laboratory materials which involves :

1. hot air sterilizer (oven): this is used for sterilizing all kinds of laboratory glassware, such as test tubes, pipettes, Petri dishes, and flasks, it may be used to sterilize other laboratory materials and equipment that are not burned by the high temperature of the sterilizer and this is operated at temperature of 160 to 180 °C for a period 1½ hr.
2. wet air sterilizer (autoclave): this is used to sterilize most type of solid and liquid media with and without carbohydrate, gelatin media, distilled water, normal saline, rubber tubing and gloves. The autoclave is operated usually at 15 Ib. steam pressure for a period of 15 min., which corresponds to temperature of 121°C.

Filtration : some solution cannot be sterilized by heat without being greatly altered in their physical and chemical properties. Serum , antibiotics, enzymes and other preparation containing heat –sensitive compounds are best sterilized by process of filtration. The type of filters employed for this purpose include: Berkefeld Filters, Fritted – glass Filters and Porcelain or Chamberland Filters.

Chemical sterilization:  Chemicals are also used for sterilization. heating, it is not always appropriate, because it will damage heat-sensitive materials such as biological materials, fiber optics, electronics, and many plastics.

Ethylene oxide: (EO or EtO) gas is commonly used to sterilize objects sensitive to temperatures greater than 60°C such as plastics

Ozone: is used in industrial settings to sterilize water and air, as well as a disinfectant for surfaces.

Radiation sterilization: Gamma rays are commonly used for sterilization of disposable medical equipment, such as syringes, needles

Ultraviolet light irradiation (UV, from a germicidal lamp) is useful only for sterilization of surfaces and some transparent objects.